The present invention is directed to photo-active cyclopentadienylplatinum (IV) compounds, and to irradiation-curable silicone compositions containing such compounds as photo-active platinum (IV) catalysts.
Drahnak, U.S. Pat. No. 4,600,484, is directed to a hydrosilylation process involving the addition between silicon hydride compounds (i.e. compounds containing the Sixe2x80x94H moiety) and compounds containing aliphatic unsaturation. Drahnak discloses that his process is activated by actinic radiation. Drahnak uses a platinum complex having the formula,
CpPt(R)3,xe2x80x83xe2x80x83(1)
where Cp is cyclopentadienyl and R is a C1-18 aliphatic organic radical.
The Drahnak catalyst consists of a cyclopentadienyl group, Cp, eta-bonded to a platinum (IV) group, Pt(CH3)3, which is substituted with three sigma bond ed aliphatic radicals. It is al so reported in U.S. Pat. No. 4,600,484, that the cyclopentadienyl group Cp can be further modified with organosilyl groups.
Boardman et al., U.S. Pat. No. 4,916,169, shows a visible light-activated hydrosilylation process for effecting the addition of a silicon hydride to compounds containing aliphatic unsaturation. In accordance with the hydrosilylation practice of Boardman et al., a polycyclic aromatic organic compound, such as anthracene, is physically blended as a sensitizer with a photo-active platinum compound, such as shown by formula (1). Based on the theory of Boardman et al., the sensitizer effects a visible light energy transfer to further enhance the photo-activation of the platinum compound. While beneficial cure results are reported by Boardman et al., it has been found that the sensitizer is sometimes incompatible in the silicone curable silicone mixture and/or a large amount of sensitizer is required to be effective.
It would be desirable therefore to provide additional procedures for improving the efficiency of photo-activated platinum (IV) compounds as catalysts for effecting the cure of irradiation-curable silicone compositions.
Further, it would be desirable to provide photo-active platinum compounds comprising a cyclopentadienyl group chemically combined to a Pt (IV) group, which did not require the separate blending of an incompatible organic material, such as anthracene, into an irradiation-curable silicone mixture.
The present invention is based on the discovery that a cyclopentadienylplatinum (IV) compound of formula (2), having a C7-20 aromatic organic radical attached to the cyclopentadienyl is more effective as a hydrosilylation catalyst for effecting the cure of an irradiation-curable silicone mixture, than is a mixture an aromatic organic compound, for example, phenanthrene and a photo-active cyclopentadienylplatinum (IV) compound, such as shown by formula (1), which is free of aromatic substitution.
In one of its embodiments the present invention comprises platinum (IV) compounds having the formula,
[(R1)a(R2)bCp]Pt(R3)3xe2x80x83xe2x80x83(2)
where R1 is a C7-20 aromatic organic radical, R2 and R3 are each independently a C1-22 aliphatic organic radical, Cp is a cyclopentadienyl radical, xe2x80x9caxe2x80x9d is an integer equal to 1 to 3 inclusive, xe2x80x9cbxe2x80x9d is an integer equal to 0 to 3 inclusive, and the sum of a+b is equal to 1 to 4 inclusive.
In another of its embodiments the present invention comprises a method for making platinum (IV) compounds of formula (2), comprising, effecting reaction between a C7-20 aromatic substituted cyclopentadienyl species having the formula,
xe2x80x83(R1)a(R2)bCpM,xe2x80x83xe2x80x83(3)
and a platinum (IV) compound having the formula,
XPt(R3)3xe2x80x83xe2x80x83(4)
where R1, R2, R3, Cp, xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d are as previously defined, M is a metallic anion, such as lithium, and X is an anionic leaving group, such as triflate, borate, phosphate, or halogen.
In still another of its embodiments the present invention comprises irradiation-curable silicone compositions comprising,
(a) an alkenyl-substituted polydiorganosiloxane having alkenyl radicals attached to silicon by carbon-silicon bonds, where the alkenyl radicals can be in the terminal position, in the polymer backbone, or a combination thereof,
(b) a silicon hydride cross-linker, and,
(c) an amount of a photo-active cyclopentadienyl-platinum (IV) compound of formula (2) which is sufficient to convert the irradiation-curable silicone composition to a tack-free state when said composition is subjected to 240-400 nm light.
In still another of its embodiments the present invention comprises a method of coating a substrate with a cured tack-free silicone film, which comprises,
(1) applying onto the surface of the substrate to a thickness of about 0.5 to about 5 mil, an irradiation-curable silicone composition comprising,
(a) an alkenyl-substituted polydiorganosiloxane having alkenyl radicals attached to silicon by carbon-silicon bonds, where the alkenyl radicals can be in the terminal position, in the polymer backbone, or a combination thereof,
(b) a silicon hydride cross-linker, and,
(c) an amount of a photo-active cyclopentadienylplatinum (IV) compound of formula (2) which is sufficient to convert the irradiation-curable silicone composition to a tack-free state, and
(2) irradiating the surface of the applied irradiation- curable silicone composition with light in the range of 240-400 nm.
In still other of its embodiments the present invention comprises substrates coated with an irradiation-curable silicone composition and the corresponding substrates coated with the subsequently cured silicone film comprising platinum (IV) compounds included within formula (2), and any reaction products thereof which may have been formed, for example, during processing and irradiation-curing.
The photo-active cyclopentadienylplatinum (IV) compounds of the present invention are shown by the following formula,
[(R1)a(R2)bCp]Pt(R3)3xe2x80x83xe2x80x83(2)
where R1 is a C7-20 aromatic organic radical, R2 is a C1-22 aliphatic organic radical, R3 is a C1-22 aliphatic organic radical or a C6-20 aromatic organic radical, Cp is a cyclopentadienyl radical, xe2x80x9caxe2x80x9d is an integer equal to 1 to 3 inclusive, xe2x80x9cbxe2x80x9d is an integer equal to 0 to 3 inclusive, and the sum of a +b is equal to 1 to 4 inclusive. In one embodiment the photo-active cyclopentadienylplatinum (IV) compounds of formula (2) can be synthesized by effecting reaction between a C7-20 aromatic-substituted cyclopentadienyl compound having the formula,
(R1)a(R2)bCpM,xe2x80x83xe2x80x83(3)
and a platinum (IV) compound having the formula,
XPt(R3)3xe2x80x83xe2x80x83(4)
where R1, R2, R3, Cp, xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d are as previously defined, M is a metallic anion, such as lithium, and X is an anionic leaving group, such as, but not limited to, triflate, borate, phosphate, or halogen.
Among the C7-20 aromatic organic radicals shown by R1 of formula (2), there are included tolyl, naphthyl, 2-benzoylnaphthalene, thioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, anthraquinone, 1-chloroanthraquinone, acetophenone, benzophenone, 9,10-dimethylanthracene, 9,10-dichloroanthracene, biphenyl, anthracenyl, phenanthryl and pyrenyl. Further, the cyclopentadienyl compound can be substituted with an xcex75-fluorenyl group. Preferred C7-20 aromatic 10 organic radicals are naphthyl, biphenyl, anthracenyl, phenanthryl and pyrenyl.
Aliphatic organic radicals included within both R2 and R3 groups are C1-22 aliphatic moieties which can independently be the same or different, and include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, allyl, aryl-substituted aliphatic moieties including benzyl and substituted benzyl, and cycloaliphatic groups including cyclopentyl and cyclohexyl. Aromatic organic radicals included within R3 are C6-20 aromatic moieties which can be the same or different, and include, but are not limited to, phenyl, and substituted phenyl, particularly alkyl-substituted phenyl. Mixtures of C1-22 aliphatic moieties and C6-20 aromatic moieties for R3 are also within the scope of the invention. In preferred embodiments both R2 and R3 groups are independently C1-22 aliphatic moieties, more preferably independently CI1-12 aliphatic moieties, and most preferably independently C1-6 aliphatic moieties. In especially preferred embodiments of the present invention R2 and R3 groups are methyl.
Illustrative examples of the compounds of formula (2), include, [1xe2x80x2-naphthyl)-cyclopentadienyl]trimethyl platinum; [2xe2x80x2-naphthyl)-cyclo-pentadienyl]trimethyl platinum; [1-methyl-3-(1xe2x80x2-naphthyl)-cyclopentadienyl]trimethyl platinum; [1-methyl-3-(2xe2x80x2-naphthyl)-cyclopentadienyl]trimethyl platinum; [(4xe2x80x2-biphenyl)-cyclopentadienyl]trimethyl platinum; [1-(4xe2x80x2-biphenyl)-3-methyl-cyclopentadienyl]trimethyl platinum; [9xe2x80x2-phenanthryl)-cyclopentadienyl]-trimethyl platinum; [1-methyl-3-(9xe2x80x2-phenanthryl)-cyclopentadienyl]-trimethyl platinum; [1-(2xe2x80x2-anthracenyl)-3-methyl-cyclopentadienyl]-trimethyl platinum; [(2xe2x80x2-anthracenyl)-cyclopentadienyl]-trimethyl platinum; [(1xe2x80x2-pyrenyl)-cyclopentadienyl]-trimethyl platinum; and [1-methyl-3-(1xe2x80x2-pyrenyl)-cyclopentadienyl]trimethyl platinum.
The irradiation-curable silicone compositions of the present invention can be made by incorporating an effective amount of a photo-active platinum (IV) compound included within formula (2) into an irradiation-curable silicone blend comprising an alkenyl-substituted polydiorganosiloxane and a silicon hydride cross-linker. An effective amount of the photo-active platinum (IV) compound of formula (2) is an amount sufficient to provide from about 5 ppm to about 500 ppm of platinum, and preferably, about 10 to about 200 ppm based on the weight of irradiation-curable silicone mixture.
If any of the components of the irradiation-curable silicone composition is a solid or is extremely viscous, a solvent can be introduced into the composition to facilitate uniform mixing of the composition components. Suitable solvents include aromatic hydrocarbons, such as, but not limited to, xylene and toluene, aliphatic hydrocarbons, such as, but not limited to, hexane and mineral spirits, halogenated hydrocarbons, such as, but not limited to, dichloromethane, chlorobenzene and trichlorobenzene, and ethers, such as, but not limited to, tetrahydrofuran, methyltetrahydrofuran, and dioxane. From about 0.01 to about 10 parts of solvent per part by weight of the irradiation-curable silicone composition may be used. The resulting composition will generally be sufficiently pure for its intended use. However, it may be desirable to remove the solvent, if one has been employed, by any convenient means known in the art.
As used hereinafter, the expression xe2x80x9cirradiation curablexe2x80x9d refers to the ability to convert an irradiation-curable silicone composition to a non-smear, tack-free film, after it has been applied in a continuous, semi-continuous, or batch manner onto a substrate, such as a paper substrate, a plastic substrate, or a metal substrate, to a thickness of about 0.5 to about 5 mils.
Lamps which can be used to effect an irradiation cure preferably provide light in the range of about 240 nanometers (nm) to about 400 nm, and most preferably, about 240 nm to about 350 nm. Depending on lamp intensity, which can vary over about 200 watts (W) to about 600 W, a continuous application rate can vary over a line speed of about 50 feet per minute (ft/min) to about 1500 ft/min.
While a variety of irradiation-curable coating compositions are included within the scope of the present invention, a preferred variety of coating compositions are useful in the paper coating art. Accordingly, the alkenyl-containing polydiorganosiloxane, which preferably consists essentially of chemically combined dimethylsiloxy units, can be a polydimethylsiloxane having vinyl radicals attached to silicon. While vinyl radicals can be in the backbone or in the terminal position, vinyl terminated polydimethylsiloxane is particularly preferred. The vinylsiloxy unit content can be about 0.05 to about 3.5 mole percent, and preferably, about 0.14 to about 2 mole percent based on total siloxy units.
While dimethylsiloxy units are preferred, other diorganosiloxy units which can be in the backbone include for example, methylphenylsiloxy units, methyltrifluoropropylsiloxy units, and diphenylsiloxy units.
The alkenyl-containing polydiorganosiloxane can have a viscosity of about 100 centipoise to about 10,000 centipoise at 25xc2x0 C., and preferably about 150 centipoise to about 600 centipoise.
The silicon hydride cross-linker can be present in the irradiation-curable coating composition at from about 0.1 part to about 10 parts by weight, based on 100 parts by weight of the alkenyl-containing polydiorganosiloxane. The silicon hydride cross-linker can have a viscosity of about 20 to about 1000 centipoise, and preferably about 30 to about 40 centipoise, and can have about 0.04% to about 1.4% by weight of hydrogen attached to silicon.
Another embodiment of the present invention comprises a method of coating a substrate with a cured tack-free silicone film, which comprises,
(1) applying onto the surface of the substrate to a thickness of about 0.5 to about 5 mil, an irradiation-curable silicone composition comprising,
(a) an alkenyl-substituted polydiorganosiloxane having alkenyl radicals attached to silicon by carbon-silicon bonds, where the alkenyl radicals can be in the terminal position, in the polymer backbone, or a combination thereof,
(b) a silicon hydride cross-linker, and,
(c) an amount of a photo-active cyclopentadienylplatinum (IV) compound of formula (2) which is sufficient to convert the irradiation-curable silicone composition to a tack-free state, and
(2) irradiating the surface of the applied irradiation- curable silicone composition with light in the range of 240-400 nm.
Still other embodiments of the present invention comprise substrates coated with an irradiation-curable silicone composition and the corresponding substrates coated with the subsequently cured silicone film comprising platinum (IV) compounds included within formula (2), and any reaction products thereof which may have been formed, for example, during processing and irradiation-curing. Suitable substrates which can be coated with a curable silicone composition and subsequently cured silicone film include, but are not limited to, cellulose-based substrates, such as paper, preferably Glassine or super-calendered Kraft paper, and film substrates, such as polyethylene, polypropylene, and polyester, such as Mylar, and hybrid substrates, such as those comprising polyethylene-Kraft paper or polypropylene-Kraft paper. Suitable substrates also include those which are substantially non-porous, such as glass or metal.